The first major objective of this project is to uncover the neural mechanisms underlying the psychophysical classification of taste into primary qualities of salty, sour, bitter and sweet. Several sets of experiments will be performed to test the hypothesis that the electrophysiological non-specificity of the receptors and neurons is more apparent than real. Analyses of single unit responses will attempt to categorize them on the basis of predominant rather than exclusive sensitivity to one of the several classes of stimuli to which they may respond. Previously described interactions between units will be explored to see whether these occur systematically on the basis of the predominant sensitivity of the interacting units. The antidromic inhibitory mechanism proposed for these interactions will be further explored by intracellular recording methods to discover whether the effects occur at the nerve terminals or trans-synaptically in the receptor cell. Electron micrographs will be examined for changes in the synaptic vesicle content of the nerve terminals after electrical antidromic stimulation. Necturus and spider will be studied because of their particular advantages of cell size and receptor isolation, respectively. The second major objective is to study the affective component of the taste response. This will be done by studying the neural mechanisms associated with the gastric secretory response to taste stimulation. The neural pathway for this reflex response will be mapped and the parameters of the taste stimulus that determine the response will be studied in chronic and acute cats.